Most Helpful Girl
Humans are just animals after all.
Fertility is a big advantage for young girls. Guys consciously or subconsciously want a girl that is going to be a fit mother for his kids. Even if the couple doesn't want kids that is still a animal instinc thing.
Girls want older guys because they are most likely settle in life. They will be providers to the children and partner, plus he will protect his family better than a dumbass her same age that doesn't know shit from life.